The present invention relates to an ink-jet recording apparatus having a recording head which ejects ink droplets through nozzles by varying the amount of pressure in a pressure generating chamber, which is communicatively connected to the nozzle opening and a reservoir of ink, in accordance with print data. More particularly, the invention relates to a technique for preventing the nozzle openings from being clogged.
An ink-jet recording head of the on-demand type includes many nozzle openings and pressure generating chambers associated with the nozzle openings. The pressure generating chambers expand and contract in accordance with print signals, to eject ink droplets through the nozzle openings. In the recording head, fresh ink is successively supplied to selected nozzle openings for carrying out a printing operation. Accordingly, there is little chance that those nozzle openings will become clogged. On the other hand, the nozzle openings that are infrequently used to eject ink droplets, such as those orifices located at upper and lower ends of the recording head, frequently clog. This is a problem.
To overcome this problem, after the printing operation is continued for a predetermined period of time, a flushing operation is performed in which the recording head is returned to the capping means in a nonprint area, and a drive signal is applied to the piezoelectric transducers, to eject ink droplets forcibly through all of the nozzle openings toward the cap.
In performing the flushing operation, the printing operation is interrupted, thereby decreasing the printing speed, and consuming a relatively large amount of ink. To solve these problems, many techniques have been proposed. According to one technique, a drive signal having an amplitude as not to eject ink droplets is applied to the piezoelectric transducers provided in the pressure generating chambers communicatively connected to the nozzle openings which eject no ink droplets during the printing operation. By the application of such a drive signal, the meniscuses present near the orifices are minutely vibrated, to thereby prevent the orifices from being clogged (See, for example, Japanese Patent Laid-Open Publication Nos. Sho. 55-123476 and 57-61576, and U.S. Pat. No. 4,350,467 989).
In this connection, a proposal has been made for a bubble jet recording head, in which the pressure applied to eject ink droplets depends on the evaporation of ink. According to this proposal, a piezoelectric transducer is attached to the reservoir, wherein the ink pressure is varied by the transducer. A varied pressure is transmitted through the ink supply port to the pressure generating chamber, to thereby minutely vibrate a meniscus formed at the nozzle opening.
Thus, by minutely vibrating the meniscuses at fixed time intervals, the number of flushing operations is reduced, thereby preventing the decrease of the printing speed and the increase of the ink consumption. Moreover, this method substantially eliminates the possibility that the nozzle openings will become clogged. However, by vibrating the meniscuses even minutely adversely affects the discharging operation of ink droplets when forming dots in a print operation. This deteriorates the print quality and is thus a problem. Moreover, the audible sound caused by the minute vibration of the meniscuses is noisy, because the number of piezoelectric transducers being driven is considerably larger than the number for discharging ink droplets. Because of this, the lifetime of the piezoelectric transducers is reduced and hence the lifetime of the recording head is also reduced.
Where the type of ink used is suitable for printing very small dots and likely to form a film, the minute vibration of the meniscuses (for the purpose of preventing the nozzle openings from clogging) promotes the volatilization of the ink solvent in the nozzle openings which are not used for printing in a printing operation, and helps the progress of the clogging of the nozzle openings. Since the viscosity of the ink depends largely on temperature, if the ambient temperature rises the ink viscosity decreases, and the minute vibration excessively moves the meniscus, so that ink wets the nozzle plate. The result is to deviate the flying path of the ink droplet when it ejects for printing.
Accordingly, a first object of the present invention is to provide an ink-jet recording apparatus which can prevent the nozzle openings from being clogged, and maintain very high print quality even with residual vibration of the minute vibration of the meniscuses.
A second object of the present invention is to provide an ink-jet recording apparatus which can reliably eliminate the clogging of the nozzle openings by reducing the frequency of vibrations of the piezoelectric transducer.
A third object of the present invention is to provide an ink-jet recording apparatus which can maximize the time until the nozzle opening becomes clogged, independently of a variation of the ambient temperature and without deviating the flying path of the ejecting ink droplet.
According to the above and other objects of the present invention, there is provided an ink-jet recording apparatus having an ink-jet recording head including pressure generating chambers each communicatively connected to a nozzle opening and a reservoir, pressure generating means for pressurizing the pressure generating chambers, and control means for applying drive signals corresponding to print data to the recording head and for minutely vibrating the meniscuses in the nozzle openings to such an extent as to not eject ink droplets during a nonprint period. The improvement is characterized in that the control means eject ink droplets from the nozzle openings in accordance with print data every print cycle during a print period, and minutely vibrates the meniscuses a preset period of time before the discharging of the ink droplets or a preset period of time after the discharging of the ink droplets.